New concepts in population genetics call for reappraisal of plant breeding procedures; this commentary evaluates certain breeding procedures according to their probable effectiveness in promoting maximum gene recombinations and achieving maximum fitness. Breeding is viewed as an accelerated evolutionary process where appropriate design and control substitute for long duration of complex interactions of genotype with environment in the wild state. Crossing selected sibs in early generations is a means of re-assembling adaptive genes capable of functioning in a balanced polygenic system. The probability that any one individual in early generations after a cross would carry all or most of the potentially co-adaptive genes is very remote; hence strict inbreeding or pure line selection from early generations will not produce the best balanced genotypes. The recombination of two or more partly balanced genotypes by sib crossing magnifies the chance that a maximum number of harmoniously functioning genes will be assembled and through subsequent inbreeding emerge as stable and widely adapted varieties. Breeding procedures are viewed in perspective as they proceed from maximum inbreeding to maximum interbreeding or from pure line selection to bulk selection with natural or enforced sib-crossing.

Plant breeding systems

Genes transformed into plants are usually inherited in a regular Mendelian manner. There are, however, transformants in which the selectable trait fails to segregate as expected. Genetic analysis of the kanamycin-resistance (KanR) trait in >900 independent transformants of Arabidopsis revealed that 9% produced progeny families with an enormous deficiency of KanR individuals. Self-pollination of individual KanR plants from these families revealed lines that continued to segregate for a deficiency of KanR seedlings. In subsequent generations, the segregation ratio in these families stabilized at approximately 1 KanR:3 KanS. Molecular analyses showed that the deficiency of KanR individuals reflected the complete absence of the introduced DNA. Reciprocal backcrosses to untransformed plants showed unequal transmission of the KanR trait through the gametes in these exceptional lines. In five cases, this was primarily a failure of transmission through the microgametophyte (pollen) and in the other two cases, primarily a failure of transmission through the megagametophyte (embryo sac or egg). The number of seeds per silique was reduced by 50% in the latter two lines. We conclude that our exceptional transformants contain T-DNA insertions that delete or disrupt genes essential for gametophytic growth and development.

https://www.genetics.org/content/genetics/147/3/1411.full.pdf

Exceptional Segregation of a Selectable Marker (KanR) in Arabidopsis Identifies Genes Important for Gametophytic Growth and Development

Phenotypic, genetic and genomic consequences of natural and synthetic polyploidization of Nicotiana attenuata and Nicotiana obtusifolia

Interspecific and Intergeneric Hybridization

The principle factors related to the banana breeding are described: botanic classification, cultivars, origin and evolution of the banana, reproductive systems, sterility and partenocarpy, polyploidy, inheritance of characteristics. To solve the problems caused by fungus, bacteria, virus, nematodes and insects, high stature and low productivity of some cultivate, it has been used the creation of new resistant varieties by means of the genetic program. The breeding program consisting of the following stages: formation, characterization and evaluation of wide germoplasma collection, introduction and selection of clones, improvement for hybridization, improvement for mutation, somatic hybridization and genetic transformation. The principle results obtained in the breeding program are: the morphologic characterization of the germoplasma, allowing the identification of promising genotypes and its recommendation to the producers; the obtainment of resistant hybrid tetraploid (Pome type) to the yellow and black sigatokas and to the Panama disease, with reduced stature and cycle and high productive; the genetic improvement of diploid AA, whose pollen has been used in the improvement of the commercial cultivars and for the own hybrid diploid; the evaluation of the cultivars and hybrid in different ecosystems, allowing to identify potential varieties to be recommended as a local and national status for several ecosystems; obtainance of hybrid of Silk cultivar (AAB) with the diploid (AA) ‘Lidi’, by means of the employment of somatic hybridization for eletricfusion, although, none cultivar was obtain from this technique.

Fred C. Elliott

Papers

Plant breeding and cytogenetics.